Joe Willis, getting upended while making a save against Vancouver last month, has been solid in goal backing up Bill Hamid and all around him United’s defense has been steadily improving. (Rich Lam/Getty Images)

D.C. United addressed several voids during the winter, but when the MLS season commenced, the defense fell under the most stringent inspection.

Would the club reduce the number of goals conceded, which was the fourth-highest count in the league in each of the past two seasons? Would the acquisition of veteran right back Robbie Russell fill the void left by Perry Kitchen, who was transitioning into defensive midfield?

And would Argentine Emiliano Dudar provide a physical central presence, adapt to a new league and, just as critically, learn English well enough to lead the back line?

The first two matches provided troubling answers as Kansas City scored a last-minute goal and Los Angeles pierced United’s tame resistance. But in the last three outings, with Dudar introduced into the lineup and the entire team embracing greater defensive responsibilities, United (1-2-2) has yielded just one goal.

And that one blemish, against FC Dallas two weeks ago, should have been ruled offside, according to officiating supervisors who reviewed the play days later.

“It wasn’t going to happen overnight,” center back Brandon McDonald said of the defensive evolution. “We had some new elements in our team. It’s coming along, slowly but surely. The chemistry is getting stronger.”

United’s improvement hasn’t come without peril. In the 4-1 victory over Dallas, Joe Willis bailed out United with two one-on-one saves while the match was scoreless. Last weekend, Seattle’s Marc Burch hit the crossbar in the dying moments.

All the same, entering an away match Saturday against the New England Revolution (2-3-0), United is better organized and becoming more difficult to infiltrate. Vancouver didn’t muster any shots on goal in a 0-0 draw, and Seattle created just two.

“Overall, our team defense has been better,” Coach Ben Olsen said. “Every guy is committed to doing both sides.”

He offered Dwayne De Rosario as an example. De Rosario is a playmaker, the club’s top scorer last year, but even he is assisting the defensive effort by pressuring opposing distributors. Olsen has also been pleased with the forwards, who have made it difficult for foes to play the ball out of deep positions, and with the wings, who have limited flank assaults.

In times of trouble, Willis has been confident and agile. With first-choice keeper Bill Hamid unavailable because of the Olympic qualifying tournament and then an ankle injury, Willis prevented an embarrassing outcome against the Galaxy and posted two shutouts.

Although Hamid traveled to New England, Olsen is expected to stick with the in-form Willis.

Daniel Woolard has been the most pleasant surprise, patrolling the left side with more composure than last year and contributing to the attack. Russell, a 12th-year pro, has provided leadership and smarts on the other corner.

McDonald (four starts), Dudar (three) and Dejan Jakovic (three) have manned the two central slots. The fourth option, Ethan White, is recovering from knee surgery. Dudar seems to have secured a starting job, leaving Olsen to choose either the physical McDonald or the nuanced Jakovic as a partner.

With Dudar able to speak only a little English, though, communication has been an issue.

“I’m picking up my Rosetta Stone today” to learn Spanish, McDonald joked Thursday. “He’s learning English. When you talk to him, he wants you to speak in English. He’s not stubborn about it. He wants to learn.”

Said assistant coach Chad Ashton: “He’s come a long way in a short amount of time. He has figured out his four or five words that he needs to be able to use on a consistent basis.”

The unit’s overall growth hasn’t been lost on the players.

“I don’t think we were all on the same page at the start of the season,” Woolard said. “It’s an understanding of each other, getting time together, and the result is, our approach has improved.”

United notes: Midfielder Marcelo Saragosa rejoined the team after missing two matches to visit an ill relative in Brazil. . . .

Third-choice goalie Andrew Dykstra was loaned to the third-division Charleston Battery for two matches. . . .

Revolution star Shalrie Joseph is serving a one-game suspension for a dangerous tackle last week.